The ornamental sweet pea, known scientifically as Lathyrus odoratus, is a popular annual flowering vine celebrated for its delicate, ruffled blossoms and intensely sweet fragrance. This plant is a favorite in gardens around the world, grown exclusively for its aesthetic appeal and perfumed air. However, despite its harmless name and beautiful appearance, the sweet pea plant is toxic if consumed.
The Definitive Answer: Toxicity Status of Sweet Peas (Lathyrus odoratus)
All parts of the ornamental sweet pea plant contain compounds that are toxic to humans and animals. The highest concentration of these harmful substances is found within the seeds and the seed pods that develop after the flowers fade. Consuming the seeds presents the greatest potential risk of poisoning.
While the foliage and flowers are not typically eaten, their consumption is strongly discouraged due to the presence of these same toxic compounds. Ingestion of a very small amount, such as a single seed by a child, is often considered a low-risk scenario that may cause mild stomach upset. The true danger lies in regular or large-quantity consumption, which can lead to a serious and debilitating condition.
The Specific Danger: Understanding Lathyrism
The toxicity within Lathyrus odoratus is caused by specific amino acids known as lathyrogens, most notably beta-aminopropionitrile (BAPN). This compound acts by interfering with a biological process that builds connective tissues throughout the body. BAPN inhibits the enzyme lysyl oxidase, which is necessary for the proper cross-linking of collagen, a structural protein.
Ingestion of the sweet pea toxin causes a condition known as osteolathyrism, which primarily targets the skeletal system and connective tissues. Symptoms typically include skeletal deformities, joint pain, and developmental issues in children. A related condition, angiolathyrism, can also occur, affecting blood vessels and potentially leading to a dangerous loss of elasticity in the aorta.
It is important to differentiate this from neurolathyrism, a paralytic disease caused by a different lathyrogen (ODAP) found in other Lathyrus species, such as the grass pea (Lathyrus sativus). The sweet pea’s BAPN toxin targets the structural components of the body rather than the central nervous system neurons. A toxic dose requires sustained consumption of the seeds over a period of time.
Avoiding Confusion with Edible Garden Peas
Much of the confusion surrounding the sweet pea’s edibility stems from its close relationship to the garden pea, Pisum sativum. These two plants belong to different genera within the same family. The garden pea, which provides the common peas found in grocery stores, is entirely safe to eat.
A clear visual distinction exists between the two plants that helps prevent accidental poisoning. The ornamental sweet pea (L. odoratus) is characterized by showy, highly fragrant flowers that bloom in a wide variety of colors, and its stems often have a distinctive winged or flattened appearance. Conversely, the edible garden pea (P. sativum) produces smaller, plainer, and less fragrant white or purple flowers, and its stems are typically rounder and more succulent.
The seed pods also differ significantly; the ornamental sweet pea pod is generally tough, sometimes fuzzy, and is not meant for consumption. The pod of the garden pea is smooth, tender, and contains the edible seeds we commonly enjoy. Gardeners should always confirm the exact species they are growing, and never consume any pea variety grown solely for ornamental purposes, even if the plant parts appear similar to those of a vegetable.